A suction control valve is used in a scroll compressor to control fluid flow between an intermediate chamber and a suction chamber to regulate compressor operation. The valve has a piston that slides in a cylinder with a sidewall opening providing a fluid passageway from the intermediate chamber into the cylinder. A top cylinder wall opening provides a fluid passageway from the cylinder to the suction chamber. As the piston slides, the size of the sidewall opening changes to regulate the volume of fluid. Changing the size or shape of the opening while fluid is flowing creates turbulence in the flow which interferes with precise regulation of the compressor.
The piston is biased by a coil spring seated against the piston. The piston normally has a stepped surface with sharp corners to retain the spring on the piston. Fluid flowing through the cylinder travels over the stepped surface and suffers from this stepped non-aerodynamic shape and realizes higher flow losses. High flow loss is undesirable because it makes compressor regulation more difficult.
A considerable fraction of flow occurs through the cylinder port and interacts with the suction control valve. Experimentation and physics do prove that this flow interaction with the suction control valve is critical to compressor operation. It is therefore desirable to make the interaction surface of the suction control valve aerodynamic in nature.